Future Therapy for End-Stage Kidney Failure: Gene-Edited Pig Kidney Xenotransplantation

Abstract

In patients with end-stage kidney disease, kidney transplantation from a living or deceased human donor offers a much-improved quality and length of life. Gene-edited pigs might provide an alternative source of kidneys for clinical transplantation (xenotransplantation). The major pathobiological barriers to successful pig kidney xenotransplantation have steadily been overcome by the following methods: (1) genetic engineering of the organ-source pig and (2) the administration of novel immunosuppressive agents. Pig kidney transplants have now supported immunosuppressed (anephric) nonhuman primates for periods in excess of a year, although this cannot be achieved consistently. The pig kidney graft can fulfill almost all of the functional requirements of a human kidney. The potential risks of infection with a pig microorganism will be minimized by the breeding and housing of the organ-source pigs in biosecure "clean" environments. For the first formal clinical trial, we suggest that diabetic patients on the waiting list aged 55-65 years with blood group O or B who are unlikely ever to receive a deceased human donor kidney might accept a pig kidney if it will negate the need for dialysis for 1 or more years.

Keywords: Immune response; gene-edited; inflammation; nonhuman primate; pig; xenotransplantation.

Figure 1

Antibody-mediated rejection in a pig kidney xenograft in a nonhuman primate. (A) Antibody-mediated rejection showing glomerular intracapillary thrombi. Other capillaries of the glomerulus show congestion, fibrin and segmental endothelial swelling, and cell loss (hematoxylin and eosin, x400). (B) C4d deposition is present along peritubular and glomerular capillaries (C4d immunoperoxidase, x200).

Figure 2

Pig kidney graft survival in baboons receiving either conventional (tacrolimus based; Group A) or anti-CD40 mAb--based (Group B) immunosuppressive therapy. Median pig kidney graft survival in Group B (186 d) was significantly longer than that in Group A (13 d) (P < 0.01) (reproduced with permission from Yamamoto et al³⁷).

Figure 3

Human (top) and Old World Monkey (OWM) (bottom) IgM (left) and IgG (middle) binding and complement-dependent cytotoxicity (CDC, at 25% serum concentration) (right) to WT, GTKO, and TKO pig peripheral blood mononuclear cells. Results are expressed as mean ± standard error of the mean (∗P < 0.05; ∗∗P < 0.01; NS = not significant). On the y axis, the dotted line represents the cutoff value of binding (relative geometric mean [GM]: IgM 1.2 and IgG 1.1), below which there is no binding. For CDC on the y axis, the dotted line represents the cutoff value of cytotoxicity (6.4%), below which there is no cytotoxicity (note the difference in scale on the y axis between IgM and IgG) (reprinted with permission from Yamamoto et al⁴⁹). Abbreviations: GTKO, α1.3-galactosyltransferase gene knockout; Ig, immunoglobulin; TKO, triple knockout; WT, wild type.

Figure 4

Comparison of mean serum IgM (left)/IgG (middle) binding and serum complement-mediated cytotoxicity (CDC, right) of baboons (n = 72) to GTKO, GTKO/β4GalNT2KO (DKO), and TKO pig peripheral blood mononuclear cells. On the y axis, the dotted line represents the cutoff values (IgM [rGM] 1.2; IgG [rGM] 1.1; CDC 6.4%), below which there is no binding or cytotoxicity. The red lines indicate the mean values (∗P < 0.05; ∗∗P < 0.01; ns = not significant). IgM and IgG binding and serum cytotoxicity to TKO cells were higher or comparable to binding to GTKO cells. Although mean IgM and IgG binding and mean serum cytotoxicity to DKO cells were less than that to TKO cells, many baboons had a high level of cytotoxicity to DKO cells (∗∗P < 0.01) (reproduced with permission from Cui et al⁵⁰). Abbreviations: DKO, double knockout; GTKO, α1.3-galactosyltransferase gene knockout; Ig, immunoglobulin; rGM, relative geometric mean; TKO, triple knockout.